JPH0820588B2 - Image detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is applied to an autofocus device of a microfilm reader that performs focus determination using an image sensor such as a CCD line sensor, and precedes the autofocus operation. The present invention relates to an image detection method for determining an image area suitable for an autofocus operation.

(Technical background of the invention) Various autofocus methods using an image sensor such as a CCD line sensor have been proposed. However, this autofocus operation is premised on that the projection light of the image area suitable for the operation is input to the image sensor. For example, a correct autofocus operation cannot be performed in an image area having a single lightness or an area in which the density changes less frequently, which causes a malfunction.

Therefore, various methods for determining whether or not the image area is suitable for autofocus prior to the autofocus operation have been proposed. For example, there is a method in which the output signal of the line sensor is binarized at a predetermined binarization level, the number of times of polarity reversal, in other words, the number of black and white reversals is calculated, and if there is a predetermined number of times or more, an image exists. However, with this method, it is difficult to obtain an appropriate binarization level for the background density of the image, correct operation cannot be expected when the focus shift of the projection lens is large, and if there are dust or scratches on the image, There was a problem that it was directly affected by the influence and was likely to malfunction.

Also, for images with negative / positive polarity, such as images from a reader / printer, it is necessary to set the binarization level separately according to the polarity, so this polarity is automatically identified and used. There was also a problem that the person had to manually input.

(Object of the Invention) The present invention has been made in view of such circumstances,
When the image area suitable for the autofocus operation is obtained prior to the autofocus operation of the microfilm reader, the background density varies greatly depending on the image, the lens is out of focus, or the image has dust or scratches. A first object of the present invention is to provide an image detecting method capable of always accurately determining an area including an image suitable for autofocusing even if there is.

A second object of the present invention is to provide an image detection method that can cope with the negative / positive polarity change in the original image, such as a microreader printer, without the need to determine or input the polarity. And

(Structure of the Invention) According to the present invention, a first object is to use an output signal of an image sensor obtained by scanning an image area of a part of the image projection light set by the zone setting means, An image detection method applied to an autofocus device of a microfilm reader that controls a projection lens to a focus position, and an image detection method for determining an image area suitable for the autofocus operation prior to the autofocus operation, the output signal of the image sensor This is achieved by an image detection method characterized in that a histogram showing the number of pixels is obtained, and an image area in which the maximum value of this histogram is equal to or less than a certain set value is set as an image area for autofocus operation.

The second invention is achieved by setting the set value so as to change as a function of the output signal.

(Principle) N-1 and P-1 in FIG. 4 show changes in the output signal V of the CCD line sensor in the micro reader printer with respect to time t, and N-2 and P-2 in the same figure show the number of pixels for the output signal. It is a histogram showing. N-1, N here
-2 is a case where the original image is a negative film, P-1 and P-2 are cases where it is a positive film.

Generally, the blackening rate of the original is about 6%, and at the highest it is 20-
30% is the limit. Therefore, on the line sensor, the number of pixels corresponding to the background is overwhelmingly large. Further, the background density is relatively stable with little fluctuation within one frame of film. Therefore, the histogram (N which indicates the number of pixels N for the output signal V (corresponding to the density D)
-2, P-2) has large maximum values A and B in the background densities D ₁ and D ₂ . If an appropriate image is not included, its maximum value is P-2 in FIG.
In FIG. 4, the image becomes extremely high, and if an image is included, it becomes low and spreads as shown by the solid line in FIGS. The area of each histogram is constant corresponding to the number of pixels of the line sensor.

Further, with respect to the image having only the background, the larger the focus shift of the lens is, the smaller the variation in the density is, and therefore the maximum values A and B of the histogram are high. On the other hand, the increase of the maximum value with respect to the focus shift is not so large for an image including many images.

Furthermore, dust and scratches on the image often have a density that deviates from the peak peak of the histogram, and even if this density may overlap the peak peak, the number of pixels can be ignored compared to the peak value. Since it is so small, the maximum value of the histogram is not affected by these dusts and scratches.

The first invention pays attention to such a point, and an image is present when the maximum value of the histogram is equal to or less than the set value h set to a negative and a positive respectively, and no image is present when the value is equal to or more than the set value h. It is what

For negative and positive images, the negative histogram a is generally located on the left side of the positive histogram b as shown in FIG. 5, and its maximum value is also large.

The second invention focuses on this point, and by setting the set value h to a function of descending to the right as shown by h ₁ or a function of decreasing stepwise as shown by h ₂ , The presence or absence of an image can always be properly discriminated without discriminating the polarity or manually inputting the polarity.

(Embodiment) FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of its autofocus control device, and FIG. 3 is a flow chart of its operation.

In FIGS. 1 and 2, reference numeral 10 is an original image of a micro photograph such as a micro fish or a micro roll film. 12 is a light source, and the light from the light source 12 is a condenser lens 1
It is guided to the lower surface of the original picture 10 through 4, the heat insulating filter 16 and the reflecting mirror 18. In the reader mode, the transmitted light (image projection light) of the original image 10 is guided to the transmissive screen 28 by the projection lens 20 and the reflecting mirrors 22, 24 and 26, and this screen 28
An enlarged projection image of the original image 10 is formed on. In the printer mode, the reflecting mirror 24 is rotated to the imaginary line position in FIG. 1, and the projection light is guided by the reflecting mirrors 22, 30 and 32 to the slit exposure type printer 34 of the PPC system. The reflecting mirrors 22 and 30 move in synchronization with the rotation of the photosensitive drum 36 of the printer 34, and a latent image is formed on the photosensitive drum 36. This latent image is visualized with toner charged to a predetermined polarity, and this toner image is transferred to the transfer paper 38.

Reference numeral 40 denotes a zone setting means, which includes a mark 42 indicating a focus zone and a manual knob 44 for moving the mark 42 on the screen 28. The position a of the zone is detected by the position detector 46 and sent to the control means 48.

A focus control optical system 50 includes a semi-transparent mirror 52 arranged on the optical axis of the image projection light, a projection lens 54, a CCD line sensor 56 as an image sensor, and a servo motor 5.
8 and. A part of the projection light that has passed through the projection lens 20 is guided to the line sensor 56 through the projection lens 54 by the semitransparent mirror 52. The line sensor 56 is movable by a motor 58 in a direction orthogonal to the optical axis. Also projection lens 54
Has a focal length such that when the projection lens 20 is placed at a position where the projection light is focused on the projection surface of the screen 28 or the photosensitive drum 36, an image is accurately formed on the light receiving surface of the line sensor 56. It has been decided.

The autofocus mechanism is equipped with a servomotor 60 that moves the projection lens 20 back and forth in the optical axis direction, and the projection light is a screen.
The focus is controlled by the control means 48 so that an image is correctly formed on the projection surface of the photosensitive drum 36 or the photosensitive drum 36.

The control means 48 is constructed as shown in FIG. That is, the CCD is synchronized with the clock pulse output from the clock 62.
The driver 64 drives the line sensor 56. The line sensor 56 outputs a pulse voltage that changes in voltage corresponding to the amount of incident light of each pixel for each scanning. This pulse voltage is
Even if the same amount of light is projected due to variations in the characteristics of each pixel, it varies for each pixel. The signal processing circuit 66 corrects the variation of this characteristic of each pixel and shapes the waveform to obtain the output signal V of N-1 and P-1 in FIG.

The output signal v thus processed is A / D converter 68.
Is converted into a digital signal by and input to the CPU 72 via the input interface 70. In FIG. 2, 74 is a ROM for storing the control program of the CPU 72, 76 is a RAM, 78 is an output interface, 80 and 82 are D / A converters, and 84 and 86 are drivers for driving the motors 58 and 60, respectively. .

Next, the operation of this embodiment will be described. The control means 48 first reads the position a of the zone set by the zone setting means 40, and the projection light of the area corresponding to this zone is read by the line sensor.
The servo motor 58 is controlled so as to be incident on 56. The user selects the reader mode with the reflecting mirror 24 in the position shown by the solid line in FIG. 1 and projects the target original image on the screen 28 (step
100). A part of this projection light is guided to the line sensor 56 by the semi-transparent mirror 52.

The control means 48 then reads and stores the output signal V of the line sensor 56 (step 102), while the output signal V
The exposure amount is measured based on the above (step 104). That is, the output signal v of the signal processing circuit 66 is read into the CPU 72 via the interface 70, and the CPU 72 controls the exposure amount. If the exposure amount is not proper (step 106), the light amount is changed (step 108), and the exposure amount is measured again. The adjustment of the exposure amount is performed by, for example, selecting the voltage of the pixel corresponding to the background area from the output signal voltage of each pixel of the line sensor 56 and adjusting the light amount of the light source 12 so that the voltage becomes a predetermined voltage. Be seen.

Next, the control means 48 determines whether or not the projection light input to the line sensor 56 includes an appropriate image. That is, based on the output signal V, the histograms shown in N-2 and P-2 of FIG. 4 are obtained (step 110), and if the maximum value is equal to or greater than the set value h (step 112), it is determined that there is no appropriate image and the control means 48 Issues an alarm such as a buzzer or lamp and requests a change of the focus zone (step 114). The user operates the knob 44 while looking at the screen 28, and moves the mark 42 so that the mark 42 overlaps a position where another image of the projected image is present. The CPU 72 moves the line sensor 56 corresponding to this new area, and repeats the operations from step 102. If the maximum value of the histogram is less than or equal to the set value h, it is determined that there is an appropriate image (step 116), and the control means 48 scans the line sensor 56 once again and performs autofocus control based on the output at that time (step 118). .

Various autofocus control methods can be applied. For example, the position of the projection lens 20 having the maximum contrast is obtained from the output signal V and the position is focused (steps 120 and 122).

If the printer mode is set in this focused state (step 12
4), the reflecting mirror 24 is rotated to the phantom line position in FIG.
The image is transferred to and a hard copy is obtained.

In the above embodiment, the maximum value of the histogram is compared with the fixed set value h, but the present invention may set the set value h as a function of the output signal V as shown in FIG.
For example, the characteristic on the right side of the drawing h ₁ or the stepwise characteristic of h ₂ can be used. In this way, an appropriate setting value h can always be automatically obtained for the negative / positive of the original image, so that the image can always be accurately detected without discriminating the negative / positive or manually inputting.

In this embodiment, all the calculations are digitally processed by the CPU 72, so that the hardware configuration can be made very simple.

Further, in the present embodiment, the focus zone is configured such that the user manually changes it with the knob 44 while looking at the screen 28, and the line sensor 56 moves accordingly, but the manual zone of the mark 42, the knob 44, etc. CP without setting method
In accordance with a command from U72, the motor 58 may be driven to automatically change the focus zone when there is no image.

The image sensor is not limited to the CCD line sensor, but may be a MOS type line sensor or an area sensor.

(Effect of the Invention) As described above, the first invention of the present invention obtains a histogram of an image sensor output signal, and determines that an image suitable for autofocus is present if the maximum value of this histogram is equal to or less than a certain set value. Therefore, even if there is a large variation in background density for each image, if there is a large focus shift, or if the image contains scratches or dust, it is possible to accurately determine whether or not the area includes the image suitable for autofocus. I can judge. Further, in the second invention, since the set value is changed as a function of the output signal, the same effect as that of the first invention is obtained, and the image is always detected correctly even if the polarity of the original image is negative / positive change. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of its autofocus control device, FIG. 3 is a flow chart of operation, and FIG. 4 is for explaining the principle. FIG. 5 is a diagram showing the output signal of the image sensor and its histogram, and FIG. 5 is a diagram of the same histogram. 10 …… original image, 20 …… projection lens, 40 …… zone setting means, 56 …… one-dimensional solid-state image sensor, h, h ₁ , h ₂ …… set value.

Claims (2)

[Claims] 1. A microfilm for controlling a projection lens to a focus position by using an output signal of an image sensor obtained by scanning a partial image area of image projection light set by a zone setting means by an image sensor. An image detection method applied to an autofocus device of a reader for determining an image area suitable for an autofocus operation prior to the autofocus operation, in which a histogram showing the number of pixels for an output signal of the image sensor is obtained, An image detection method characterized in that an image area having a maximum value equal to or less than a certain set value is used as an image area for autofocus operation. 2. A microfilm for controlling the focus position of a projection lens by using an output signal of the image sensor obtained by scanning an image area of a part of the image projection light set by the zone setting means by the image sensor. An image detection method applied to an autofocus device of a reader for determining an image area suitable for an autofocus operation prior to the autofocus operation, in which a histogram showing the number of pixels for an output signal of the image sensor is obtained, An image detection method characterized in that an image area for autofocus operation is set using an image area whose maximum value is equal to or less than a set value set so as to change as a function of the output signal.